Sacroiliac (SI) joints are formed by the connection of the sacrum to the ilium bones of the pelvis. There are two SI joints in the human body; one on the left and right sides, respectively of the lower spine. Sacroiliac joints are diarthrodial, meaning they allow motion between the bones they connect. Additionally, SI joints are weight bearing, meaning a primary function of the joint is to absorb shock and provide just enough motion and flexibility to lessen stress on the pelvis and spine. In women, the SI joints are weaker, in part, probably, because the SI joints relax during the end stages of parturition, or childbirth. The joints can become painful for a number of reasons including, but not limited to, arthritis, abnormal leg alignment, pregnancy leading to increased stress on the joints, or any condition which alters the normal walking pattern and/or stresses the joints including trauma, infection, cancer, and spinal instability. In the early 1900's the exact causes of back pain were unknown but, there were a number of possible causes including dysfunction of the SI joint. In 1934, Mixter and Barr proclaimed that back pain could result from a posterior rupture of an intervertebral disc. Mixter W J, Barr J S. “Rupture of the intervertebral disc with involvement of the spinal canal.” N Engl J Med 1934; 211:210-5. Due to Mixter and Barr's paper, physicians began to consider degenerative disk disease and disk herniation as the primary causes of back pain over SI joint dysfunction. Today, it is believed that approximately 20% of low back pain is SI joint related. There are a number of misdiagnoses of back pain due to the variety of possible causes.
SI joint pain can be treated non-surgically and surgically. One nonsurgical option for pain relief involves the injection of a corticosteroid into the joint, which reduces inflammation of the joint. Another nonsurgical option for pain relief is the use of oral anti-inflammatory medications such as non-steroidal anti-inflammatory drugs (NSAIDS), ibuprofen, and naproxen to reduce inflammation of the painful joint. Physical therapy, yoga, and Pilates can also help relieve pain associated with the SI joint because pain can result from excessive or insufficient motion in the joint. Some patients benefit from wearing a special brace called a sacroiliac belt, which wraps around the hips to hold the SI joint tightly together. This belt can help decrease inflammation of the SI joint.
If non-surgical treatments fail to treat the pain associated with the SI joint, the pain can also be treated surgically by fusing the joint(s). This surgical fusion is also known as arthrodesis. In this surgery, the cartilage covering the surfaces of the SI joints is removed and the bones are held together with plates and screws until they grow together, or fuse. Percutaneous sacroiliac joint fusion is a minimally invasive approach in which cages or screws are placed, with or without bone graft, to achieve a fusion. Smooth or threaded metallic bone fastener devices have been used to achieve a fusion and such devices include a series of metallic, porous plasma spray coated rods, which are surgically inserted across the SI joint. Other systems use cannulated screws.
One surgical implant of the cannulated screw type, found in U.S. Pat. No. 8,142,503 (Malone), has been developed, which comprises a conical hollow facet for facilitating bone growth or repair. The conical hollow facet further comprises threading for facilitating securement to bone, a port to accommodate an allen wrench, an internal cavity for bone morphogenic protein, and a plurality of orifices for facilitating delivery of the substance within the cavity to adjacent bony structures. The facet disclosed also includes a member, which seals the hollow cavity to prevent desired substances from escaping from within the cavity. This reference fails to disclose an open-ended surgical implant having apertures for ancillary screws.
Another surgical implant is disclosed in the Michelson family of patents (U.S. Pat. No. 6,558,423; U.S. Pat. No. 7,033,394; U.S. Pat. No. 7,041,135). The implant disclosed in the Michelson family of patents comprises a cylindrical perforated hollow body having a leading end and a trailing end, holes for the growth of bone and vascular access, and a constant diameter of the screw threading along the length of the cage. The trailing end of the implant further comprises holes to receive a bone screw such that the bone screw would be directed first through the trailing end and then through either one of upper or lower vertebral bone engaging surfaces of the implant and finally into the vertebral body at an angle. This reference fails to disclose a percutaneous sacroiliac joint fusion implant, which comprises an open-ended tapered screw arranged to receive at least two ancillary screws, which can be tapped to determine the trajectory of the ancillary screws while the ancillary screws are engaged with the tapered screw.
United States Patent Application Publication No. 2004/0147929 (Biedermann et al.) discloses yet another surgical implant which comprises a middle conical bone-threading section tapering towards an end and apertures therein which allow for the growing-in of bone material or vessels. This reference fails to disclose an open-ended surgical implant having apertures for ancillary screws.
United States Patent Application Publication No. 2011/0230884 (Mantzaris et al.) discloses a polyaxial screw device to be inserted into a bone structure comprising a tapered screw member, which is cylindrical and has a substantially smooth exterior surface, a threaded portion, and tapered apertures to accommodate lag screws. This reference fails to disclose an open-ended surgical implant having apertures for bone fusion promoting substances and apertures for ancillary screws.
Despite these attempts, surgical treatment of the SI joint has still been problematic because the joint is very deeply located in a region of the human body. Percutaneous surgical implants used on the SI joint have a high rate of screw malpositions, which may be associated with risk of neurologic damage or inefficient stability. Additionally, over time if the SI joint does not completely immobilize because of a percutaneous surgical implant, the spine can shift, the implants can loosen, and pain can result again. Thus, a need has existed for an accurate and effective surgical implant for the fusion of the SI joint.